Introduction To Periodic Motion

We can classify the motion of various bodies on the basis of the way they move. For example, a car moving on a straight road is said to have linear motion. Similarly, the motion of the earth around the sun is circular motion. Here we will be talking mainly about periodic motion. A motion that repeats itself after equal intervals of time is known as periodic motion. Examples of periodic motion are a tuning fork or motion of a pendulum if you analyze the motion you will find that the pendulum passes through the mean position only after a definite interval of time. We can also classify the above motion to be oscillatory. An oscillatory is a motion in which the body moves to and fro about a fixed position. So an oscillatory motion can be periodic but it is not necessary.

So taking an example of a wave motion we will see some of the parameters related to periodic motion. Let’s take the following figure:
Periodic Motion

Periodic Motion Formula

Time Period (T): It is the time taken by the motion to repeat itself. So the unit of a time period is seconds.
Frequency (f): It is defined as a number of times the motion is repeated in one second. The unit of frequency is Hz (Hertz). Frequency is related to Time period as:

\(f=\frac{1}{T}\)

Above is the formula used for periodic motion.

Simple Harmonic Motion

We also have heard of something known as simple harmonic motion. What is a simple harmonic motion? It is actually a periodic motion having some relation between the restoring force and displacement from the mean position. We will be discussing this motion in detail you can take a look at the introduction to SHM.

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Practise This Question


In which of the cases, the ball supposed to be in Equilibrium, if net force on ball in each case is zero. (Here we are only talking about translation equilibrium, not rotational)